1. FIELD OF THE INVENTION
The present invention relates to an art for controlling displacement of a swash-plate type compressor which is suitable for use as a refrigerant compressor of an automotive air conditioner, for example.
2. DESCRIPTION OF THE PRIOR ART
The present inventors have proposed a variable displacement swash-plate type compressor having a tiltable swash plate mounted on a shaft and arranged such that the tilting angle of the swash plate is varied in accordance with the displacement of a spool and that the position of the center of the swash plate is also controllable.
In this compressor, the tilting angle of the swash plate and the position of the center of the swash plate are both simultaneously controlled in accordance with the movement of a spool effected by a control of the pressure in a control pressure chamber which is formed behind the spool.
The present invention pertains to an improvement in the variable displacement swash-plate type compressor proposed by the present inventors. More particularly, the invention is concerned with an improvement in the control valve for adjusting the control pressure which is introduced into the control pressure chamber.
The suction pressure in this type of compressor varies according to the load applied to the refrigeration cycle, and the control valve operates in such a manner as to control the signal pressure introduced into the control chamber behind the spool in accordance with the change in the suction pressure.
Thus, the position of the spool is changed to increase or decrease the displacement of the compressor in accordance with the change in the suction pressure. In consequence, the displacement of the compressor is controlled in such a manner as to maintain the suction pressure at a constant level. The constant suction pressure of the refrigerator compressor means that the evaporation temperature of the refrigerant in the evaporator of the refrigeration cycle is held constant.
In some cases, however, a better result is obtained when the control is effected to positively vary the evaporation temperature than when the control is made to maintain a constant evaporation temperature, as in the case of a drastic change in the thermal load applied to the refrigeration cycle.
Accordingly, an object of the present invention is to provide a variable displacement swash plate type compressor in which the amount of movement of the spool is controlled basically in accordance with the change in the suction pressure of the controller and also in accordance with a signal other than the suction pressure of the compressor.